Dart Encryption/Decryption

hng_task_two.dart

import 'package:flutter/material.dart';
import 'dart:convert'; // Access to encoding/decoding


class SimpleEncryption {
  // This method takes two parameters: the text to encrypt
  static String encrypt(String text, String secretKey) {
    if (text.isEmpty || secretKey.isEmpty) {
      throw ArgumentError('Text and secret key cannot be empty'); // Checks if text and secretKey is empty
    }

    // Convert text and key into numbers from 0-255
    List<int> textCharacter = utf8.encode(text);
    List<int> keyBytes = utf8.encode(secretKey);

    // Create an empty list
    List<int> encrypted = [];

    // Encrypt each character using the key
    for (int i = 0; i < textCharacter.length; i++) {
      // Get the current key 
      int keyByte = keyBytes[i % keyBytes.length];
      
      // Add the key  to the text  and take modulo 256
      // to keep it within  range (0-255)
      int encryptedByte = (textCharacter[i] + keyByte) % 256;
      
      encrypted.add(encryptedByte);
    }

    // Convert for safe storage and transmission
    return base64Encode(encrypted);
  }

  /// Decrypts a string that was encrypted using the encrypt method
  static String decrypt(String encryptedText, String secretKey) {
    if (encryptedText.isEmpty || secretKey.isEmpty) {
      throw ArgumentError('Encrypted text and secret key cannot be empty');
    }

    try {
      // Decode the base64 string back to bytes
      List<int> encryptedBytes = base64Decode(encryptedText);
      List<int> keyBytes = utf8.encode(secretKey);
      List<int> decrypted = [];

      
      for (int i = 0; i < encryptedBytes.length; i++) {
        int keyByte = keyBytes[i % keyBytes.length];
        
        // Subtract the key byte and handle negative results
        int decryptedByte = (encryptedBytes[i] - keyByte) % 256;
        if (decryptedByte < 0) {
          decryptedByte += 256;
        }
        
        decrypted.add(decryptedByte);
      }

      // Convert back to string
      return utf8.decode(decrypted);
    } catch (e) {
      throw const FormatException('Failed to decrypt: Invalid input or wrong key');
    }
  }
}

void main() {

 runApp(
 const  MyApp()
 );
}


class MyApp extends StatefulWidget {
  const MyApp({super.key});
  @override

  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String encrypted = "";
  String decrypted = "";

  @override
  void initState() {
    super.initState();
    _encryptAndDecrypt();
  }

  void _encryptAndDecrypt() {
    try {
      String secretKey = "MyHNGTask";
      String originalText = "Hello, this is my secret message!";

      // Encrypt the text
      encrypted = SimpleEncryption.encrypt(originalText, secretKey);

      // Decrypt the text
      decrypted = SimpleEncryption.decrypt(encrypted, secretKey);

      // Update UI
      setState(() {});
    } catch (e) {
      print('Error: ${e.toString()}');
    }
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        backgroundColor: Colors.blue.shade700,
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Image.asset(
                'assets/hng_logo.jpg',
                width: 100,
              ),
              const SizedBox(height: 20),
              const Text(
                'Encrypted Text:',
                style: TextStyle(color: Colors.white, fontSize: 18),
              ),
              Text(
                encrypted,
                style: const TextStyle(color: Colors.white),
                textAlign: TextAlign.center,
              ),
              const SizedBox(height: 20),
              const Text(
                'Decrypted Text:',
                style: TextStyle(color: Colors.white, fontSize: 18),
              ),
              Text(
                decrypted,
                style: const TextStyle(color: Colors.white),
                textAlign: TextAlign.center,
              ),
            ],
          ),
        ),
      ),
    );
  }
}

🎓 My Second HNG App - Encryption and Decryption

Test & Live Demo

For the app test Click here

To check live demo Click here

Installation

1. Clone the repo

git clone https://gist.github.com/53bb49d725efb94e247c398cced27b4d.git

Rename the file as main.dart

2. Create a new flutter project

Run the following command in the command line / terminal

flutter create projectName

3. Add file to lib folder in the new Flutter project

4.

Use the command below to run the app on an emulator or connected device.

flutter run

Contribution

Contributions to the second HNG app are always welcome! If you have any improvements or features you'd like to add, fork the repository and submit a pull request.